The invention relates to a high-speed gear with oil lubrication, especially for environmentally-sealed railway driving mechanisms, with oil-recycling ducts leading out of the labyrinth chambers of contactless shaft seals to the crankcase of the gear casing.
In the lubrication of modern, high-speed railway driving mechanisms, generally the teeth of the large wheel take up oil from the crankcase of the gear casing in the manner of splash lubrication during the startup process; the driving pinion is wetted and, due to its fractured structure, a fine oil-air mixture is formed as the rpm increases. This mixture is distributed in the entire gear, and thus also lubricates the bearings of the drive shafts in the gear casing.
Assuring a reliable, no-wear and extensively oil- and gas-tight seal toward the outside at the contactless shaft seals of these bearings poses a major problem for drives with high-speed, large gears. Usually, labyrinth seals whose function lies in throttling the pressure in the gap are used. The oil mist that condenses in the labyrinth chambers of the seals is continuously removed via a siphon system, and re-circulated into the closed gear casing, which is intended to prevent a significant amount of leaked oil from exiting via the external dirt-removal chambers of the labyrinth seals. The oil-recycling conduits are sloped for this purpose, and terminate above the crankcase.
In very high-speed gears, it appears that the oil-air mixture is carried along, as a so-called drag current, at virtually the same angular speed as the large wheel in the gear casing, and is warmed considerably due to inherent friction, thereby expanding. Consequently, it has a more pronounced effect on the labyrinth seals. This requires, among other things, highly-reliable oil recycling from the labyrinth chambers of the seals to prevent the escape of oil.
To reduce the frictional heat of the oil mist to a tolerable level, it is necessary to keep the quantity of oil in the gear casing as small as possible, and thus keep the viscosity of the oil-air mixture as low as possible, and to create the smoothest possible flow conditions in the gear casing. It must also be ensured, however, that the gear absolutely not be allowed to run dry, which would lead to jamming; therefore, it is imperative that a quantity of oil required for reliable operation be maintained at all times. Hence, the oil-supply tolerances are very tight, and must be monitored diligently.
Particularly for railway driving mechanisms, but also for other applicable, high-speed gears, it is an object to improve the manner in which oil is conveyed out of the gap seals in order to prevent leaked oil to the greatest possible extent, and to create a highly-reliable, that is, sensitive and position-tolerant, oil-supply display, without significantly disturbing the flow conditions in the gear casing.
According to the invention, this object generally is accomplished by a high-speed gear arrangement with oil lubrication, especially for environmentally-sealed railway driving mechanisms, with oil-recycling ducts leading out of the labyrinth chambers of contactless shaft seals to the crankcase of the gear casing or gear box, and wherein the ends of the oil-recycling ducts leading to the crankcase terminate in regions in which a relative vacuum is automatically established during running operation, independently of the direction of rotation of the gear arrangement, with the regions with a vacuum being formed by axial narrow points or constrictions between the tooth region of the large wheel of the gear arrangement and the bordering walls of the gear casing. Advantageous embodiments likewise are disclosed.
According to the invention, the Bernoulli effect is utilized during gear operation to generate a vacuum at the termination point of the oil-recycling ducts, which effectively supports the flow of oil from the labyrinth chambers of contactless shaft seals. According to Bernoulli, the static pressure in a fast-moving fluid is lower than in a non-moving or slower fluid; specifically, the larger the flow difference, the lower the static pressure. If the region of the gear casing through which the drag current passes is artificially narrowed, the speed of the drag current increases in this region, and the static pressure drops at this location relative to the entire system. If the oil-recycling ducts terminate in such a region, an eddy is formed in the oil-recycling ducts during operation, which essentially supports the flow-off of the coil that has condensed in the seal system.
The discussed arrangement has the same physical effect as a venturi nozzle, although it is specified for a different purpose. The narrow point is advantageously created in a region of the gear casing in which the highest speed of the drag current dominates, namely near the periphery of the large wheel. A particularly well-suited location is directly above the crankcase, utilizing the guide incline of the oil-recycling ducts. If the constricted areas are formed by material buildups in the walls of the gear casing in this region, these areas can advantageously also accommodate bores for the oil-recycling ducts from the large-wheel bearing. The material buildups are preferably embodied such that the change in the cross section of the drag current is effected in both directions of rotation with the least possible eddy formation. Furthermore, a float, which is visible through a viewing glass provided for checking the oil supply, can be seated in a directly-adjacent bore. With this arrangement of the float in the built-up region of the housing wall, the flow behavior of the oil-air mixture is not disturbed in either the narrow point or in further flow-sensitive regions; additionally, the complicated tubular guides for the float that would otherwise be necessary can be omitted. Moreover, the oil level is read in this region if, in an advantageous embodiment of the invention, it coincides with the center of gravity of the surface of the permissible oil-bath level, independently of the inclination of the gear casing, as stipulated by, for example, the inclination of the extension. The oil-recycling ducts terminating here ensure that a sufficient quantity of oil is available for the float when the gear is inoperative.
For additionally utilizing the eddy effect to convey the oil out of the bearing of the drive pinion, the oil-recycling lines of the pinion can likewise terminate in the artificially-narrowed region.
The embodiment of the gear according to the invention has a very low cost and space requirement, and production is non-problematic. The device itself is maintenance-free and requires no external power. With the exception of the float, which may or may not be used to raise the reading level, no mechanically-moved parts are required. Further advantageous embodiments ensue from the dependent claims.